Attachment of fibers, and in particular single-mode fibers, to semiconductor lasers requires very accurate positioning of the fiber core with respect to the lasing spot of the laser to achieve optimal coupling of the light. The conventional technique of butt-coupling of cleaved fibers requires fiber alignment, lateral to the beam propagation direction, to within 0.5 .mu.m with respect to the laser beam center in order to ensure good coupling efficiency. The coupling efficiency can be further improved by tapering the fiber end or lensing the fiber tip. However, these modifications to the fiber further increase the precision necessary for accurate fiber alignment.
The alignment accuracy in the axial direction (along the direction of beam propagation) is more relaxed than in the lateral direction since the coupling efficiency is less sensitive to the precise distance of the fiber to laser than to the fiber lateral displacement away from the center of the laser beam. In a conventional laser-to-fiber butt-coupling assembly, for example, the positioning in the lateral y-direction is the least precise but is the most critical since the coupling efficiency is more sensitive to variations in the y-direction than in the axial x-direction. For an efficient pigtailing operation, it is desirable to locate the fiber in a fiber receiving conduit, such as a V-groove, to facilitate a permanent fiber attachment in the aligned position. Placing the fiber in such a V-groove, however, allows adjustment of the fiber position in the least critical dimension (x-direction) only, namely along the fiber axis.
In parent U.S. Pat. No. 5,163,113, filed Jul. 19, 1990, there is shown an apparatus for overcoming some of the disadvantages of the prior art by polishing the ends of the optical fibers at a 45 degree angle and having the laser beam enter the fiber at a right angle to the fiber axis. The fiber in the referenced application is positioned above a surface emitting laser source or a mirror is used to redirect the non-surface emitting laser beam into the beveled fiber. While the apparatus described in that application is a clear advance over the prior art and satisfactory for the purposes therein described, the top mounted fiber complicates design and fabrication issues. Further, the positioning of the light-emitting source on the assembly makes it relatively difficult to provide for redundancy in the event of a fabrication defect in the laser.
Thus, it would be advantageous to provide for a laser-to-fiber coupling assembly that was easier to fabricate, and allowed for a measure of redundancy in the event of a laser failure, while still employing the advantages disclosed in the referenced co-pending application.